The present invention relates to improvements to fluid actuated cylinders having a reciprocable piston member within a piston chamber, and more particularly relates to a fluid actuated damping device designed to decelerate the piston along an end portion of its working stroke, while reducing the impact forces of the piston against an end closing member of the piston chamber, at the reversal of the reciprocating movement. The invention in its various embodiments is applicable to single-acting or double-acting cylinders, both of the rod and of the rodless type.
The invention also relates to a cylinder of the kind referred to above, provided with a damping device designed to provide a prolonged deceleration effect, while keeping the same cylinder within standard dimensions.
In order to dampen and decelerate the reciprocating movement of a piston at the end of its working stroke, in hydraulic or pneumatic cylinders it is known to provide suitable pressure actuated damping means which intervene at the end of the piston stroke to prevent shock on the load connected to the cylinder or damage to the same; usually said damping means comprise a cylindrical or conical member axially extending from one end of the piston member and designed to protrude into a corresponding hole in an end member of the cylinder, so as to close a discharge outlet or define a flow passage through which the fluid under pressure is forced to pass towards a venting path for the same pressurized fluid which remains in the cylinder chamber during the final portion of the piston stroke.
Other known damping devices comprise suitable adjustable seals and needle valves for varying the air venting speed and deceleration speed of the piston.
Examples of cylinders provided with damping devices for controlling deceleration of the piston, are described in U.S. Pat. Nos. 3,440,930, 3,805,672, 3,964,370 and EP 0 005 407.
Other deceleration devices similar to those referred to above, in particular for rodless cylinders, may be found, for example, in EP 0 345 506, EP 0 082 829, U.S. Pat. Nos. 4,373,427, 4,829,881 and 4,852,465 which also illustrate the general features of a rodless cylinder.
In general, the prior known damping devices comprise a cylindrical member projecting from the piston or the closing end wall of the piston chamber to penetrate into a corresponding hole at the end of the piston stroke so as to close the direct supplying and discharging port for the fluid under pressure, allowing the said fluid to be vented through a restricted path in order to decelerate the piston.
These damping devices generally are necessary in many applications, not only in order to decelerate adequately the speed of the piston and the load connected to it, at the end of the working stroke, but also reduce the impact forces of the piston against the closing end wall, reducing the noise level thereof.
The damping devices of this kind, however, do not ensure a sufficiently effective damping effect and an adequate control of deceleration of the piston, in particular when rapid displacements of the piston are required or when the movable mass of the load to be stopped has a significant value, since they depend on the volume of fluid under pressure which can be ejected through the venting duct, during the end portion of the piston stroke.
Considering that the useful working stroke of a piston in standard cylinders cannot be modified, to improve damping by a conventional damping device it is necessary to increase the length of the deceleration stroke of the piston; this would inevitably result in an increase in the dimensions of the length of the whole cylinder, in respect to a standard one.
In an attempt to solve this problem, namely in the attempt to find a damping device for pneumatic cylinders which was able to provide a sufficiently long deceleration stroke, without increasing substantially the dimensions of the same cylinder, EP 0 648 941 proposes a particular damping device which can be used both with usual rod and with rodless cylinders, comprising a venting path which can be telescopically lengthened. However, this device also involves a considerable increase in the length of the cylinder, in addition to an extremely complex design which is difficult to apply to cylinders operating at high speeds. The length of the final stroke for the deceleration of the piston must also be suitably calculated during the designing, without any possibility for subsequent adjustments to modify or adapt the damping device.
The main object of the present invention is to provide a fluid actuated cylinder comprising a damping device to provide a controlled deceleration of the piston along a sufficiently long damping stroke, by using a consequent high volume of fluid to be vent or discharged through a restricted path, without negatively affecting the dimensions and working of the same cylinder.
A further object of the present invention is to provide a cylinder comprising a damping device, as referred to above, by means of which it is possible to keep the dimensions of the cylinder within standard values, achieving an improved deceleration of the piston and damping effect.
Yet another object of the present invention is to provide a cylinder with a damping device which is both constructionally simple and by means of which it is also possible to vary or modify the length of the deceleration portion of the piston stroke, during the designing of the cylinder, with the possibility also, in certain cases, of carrying out adjustments subsequently, during the assembling or the use.
Yet another object of the present invention is to provide a damping device for pneumatic cylinders as referred to above, which can be used both in cylinders with rods and in rodless cylinders, independently of the dimensions and the features of the cylinder itself.
The advantages which may be achieved with the present invention consist not only in the limitation of the overall dimensions of the cylinder and in a constructional simplification of the damping device, but also in the possibility of increasing the working speed of the piston, while maintaining, however, a high damping efficiency, in particular in cylinders of short-stroke type.
In particular, according to a first aspect of the invention, a fluid actuated cylinder and a damping device has been provided, the cylinder comprising a cylindrical body defining an elongated piston chamber having an inlet and outlet port for pressurized fluid opening into the piston chamber at least one end thereof; a reciprocable piston member in said piston chamber; a closing member provided on the piston member for closing the fluid inlet and outlet port, the damping device comprising said closing member and a restricted flow path for discharging the pressurized fluid upon closure of said port, wherein said closing member is coaxially arranged and movably supported by a helical spring, in respect to the piston member, and in that said piston member comprises a front open cavity at one end to receive at least a rear portion of the closing member and the helical support spring upon closure of the inlet and outlet port by said closure member, during the final portion of the piston stroke.
According to another aspect of the invention, in particular for cylinders with rods, the spring for supporting the closing member is coaxially arranged to the piston rod and the same closing member is in annular form, being slidably and axially guided along the same rod of the piston member or along an extension thereof.
According to yet another aspect of the invention, in particular for rodless cylinders, the spring for supporting the closing members freely extends from the piston end, and the closing member is in the form of a plug member provided with a peripheral flange slidably guided by the internal surface of the cylinder.